The specific aim of this research is to study in the cat certain brain stem nuclei and pathways essential for the control of eye movement. The long term goal of these experiments is to establish the neuronal operations of the vertebrate oculomotor system, especially that of its prenuclear elements during eye movement. Toward that end the specific goals of the present project period are related to ascertaining the origin and function of those brain stem nuclei utilizing principally the medial longitudinal fasciculus to regulate eye movements by either directly terminating on ocular motoneurons or indirectly by supranuclear connections through the latter areas. Morphological and physiological studies are planned to deal with major areas of uncertainty concerning vestibular, peri-hypoglossal, reticular and accessory ocular nuclei connections. The techniques to be utilized will be the standard electrophysiological ones comprising intra- and extracellular recordings from neurons and axons in anesthetized and alert cat preparations. Particular emphasis will be placed upon obtaining both anti- and orthodromic identification of central neuronal elements in the alert cat paradigm as identifcation criteria are developed from the anesthetized preparation. Morphological studies including lesion, degeneration and retrograde horseradish peroxidase will be designed to afford, via light and electron microscopy, a general picture of ocular sensorimotor organization. The studies outlined in this proposal should provide fundamental information concerning intrinsic organization of the ocular nuclei and the immediate premotoneuronal nuclei which are involved in the control of vertical and horizontal eye movement. BIBLIOGRAPHIC REFERENCES: Baker, R., Berthoz, A. and Delgado-Garcia, J. Monosynatic excitation of trochlear motoneurons following electrical stimulation of the prepositus hypoglossi nucleus. Brain Research 121: 157-161, 1977. Maciewicz, R.J., Romagno, M.A., Baker, R. and Highstein, S.M. Two projections of the oculomotor internuclear neurons. Anatomical Record 187: 642, 1977.